1. Field of the Invention
This invention relates to an improvement in a process for chemically modifying substrates to impart new properties thereto; and, more particularly, to an improved graft copolymerization process wherein a graft copolymer of such a substrate and at least one ethylenically unsaturated monomer can be obtained quite rapidly through the use of highfrequency microwave energy.
2. Description of the Prior Art
The process to which the improvement of this invention relates has been disclosed, for example, in a number of United States Patents, such as U.S. Pat. No. 3,340,326, U.S. Pat. No. 3,357,933, U.S. Pat. No. 3,359,222; and U.S. Pat. No. 3,359,224, said process being one in which a water-insoluble thiocarbonated or thiocarbamated substrate is reacted with at least one ethylenically unsaturated monomer via peroxidic free radical initiation. As indicated in each of the above-mentioned U.S. Patents, the copolymerization reaction can be conducted in either an aqueous or a non-aqueous system, but is preferably and ordinarily conducted in an aqueous system in which the monomer is uniformly distributed (cf., for example, column 9, lines 5 to 8 of U.S. Pat. No. 3,359,224). As also indicated in the above-mentioned U.S. patents (cf., for example, column 9, lines 16-41 of U.S. Pat. No. 3,359,224), the reaction conditions for this particular process are not narrowly critical, and depend to a large degree on the monomer or monomers employed and the monomer add-on desired. It should be noted, however, that when conventional batch grafting techniques are employed with mild reaction conditions (e.g. aqueous solutions, suspensions or emulsions of the monomer (s) with reaction temperatures at or about room temperature), extended periods of time are often required to obtain substantial add-ons of monomer, (cf., for example, the working examples of any of the above-mentioned patents).